1. Field of the Invention
The present invention relates to systems for detecting faults in power signals, and responding appropriately. More specifically, the invention relates to systems for detecting phase and/or amplitude faults in multi-phase power lines providing power to equipment at an installation, and responding appropriately to cut off the power to prevent damage to the equipment.
2. Related Art
Suppliers of electricity such as public electric utility companies typically provide electric power to factories and other institutions in the form of a multi-phase AC voltage. Typically, such voltage is a 50 or 60 Hz, three-phase 208/230-volt or 460/480-volt signal.
It is well known that such multi-phase AC voltage is susceptible to a variety of electrical disturbances which may damage equipment at the installation. For example, one or more phases of the voltage may experience a sudden increase or reduction in amplitude. Furthermore, "brown-outs" and power surges may occur. Also, one or more of the phases may actually drop out, or even reverse in phase. And of course, there may be a total loss of power on all phases. Each of these disturbances can induce instantaneous voltages and currents to be experienced in the equipment which can damage costly components, even if the disturbances are experienced only for a short time. The duration of disturbance which equipment can tolerate varies substantially with the type of disturbance and the particular equipment involved.
Various phase or amplitude fault detection systems are known in the art. However, such known systems have typically been unduly complex and, for at least that reason, have lacked in reliability. Further, the response of the known systems have often been inappropriate, cutting power off when such a drastic response was not warranted for a given installation, or, conversely, responding too slowly when a damaging amplitude or phase fault is encountered. Perhaps worst of all, some fault detection systems have lacked the ability to reliably detect a wide range of phase and amplitude faults, allowing continued supply of power which is damaging to plant equipment.
Thus, there is a need in the art to provide a simple, reliable, comprehensive electrical amplitude and phase fault detection and response system which detects any of a variety of amplitude and phase faults, and responds with speed and action appropriate to a particular user's site requirements.
Of equal concern to the owner of the installation equipment is the fact that, after the disturbance is experienced, the supplier may not restore electric power in its proper phases and amplitudes in a uniform manner. For example, after a total power failure, the three phases may not all be restored simultaneously. Further, the amplitudes of each phase may not be uniformly and simultaneously restored to proper levels. These occurrences are of concern, because many known fault detection and/or response systems may not operate properly long after the power failure.
In such systems, when electrical power is interrupted or disturbed to such a degree that the known fault detection or response system itself could not properly operate, the system may not continue to detect the state of the remaining power which still reaches plant equipment, possibly damaging it. Further, after a total power failure, the lack of power to the detection and response system may also lead to equipment damage in the time period immediately after power is restored but before the detection and response system begins to function.
Therefore, there is a need in the art to provide an electrical amplitude and phase fault detection and response system which allows the user to be assured that electrical power has been fully and properly restored before providing that power to plant equipment.